The research involves an analysis of the sexual preferences of recently domesticated Syrian and Turkish female hamster. In the test situation, females are allowed to choose between mature, sexually experienced males of each species. Experiment 1 investigates the nature of this selection response in estrous females of both species. Pilot work has determined that there are several species differences, including the finding that Turkish females sexually present in front of captive Turkish males wheras Syrian females never present in front of captive Syrian males. Experiment 2 examines the possibility that sexual preferences may vary with the estrous cycle. Experiment 3 seeks to determine if olfactory stimuli are sufficient to maintain sexual selection by Turkish hamsters. By using a new technique of peripheral anosmia, Experiment 4 examines the necessity of olfactory stimulation to the sexual selection behavior of Turkish hamsters. Experiment 5 investigates the possibility that sexual preferences may be eliminated or reversed by early experience obtained by being cross fostered with the other species. This research takes advantage of the availability, for the first time of two closely related species of hamsters of similar domestication history, and the fact that females of one of these species display exceptionally strong preferences for conspecific males under simple laboratory conditions.